Biasing mechanism for impact wrenches



Oct. 12, 1954 F. A. JIMERSON BIASING MECHANISM FOR IMPACT WRENCHES Filed Oct. 11, 1949 INVEN OR FRANCIS A. JIMERSON HIS ATTORNEY- Patented Oct. 12, 1954 BIASING MECHANISM FOR IMPACT WRENCHES Francis A. Jimerson, Athens, Pa., assignor to Ingersoll-Rand Company, New York, N. Y., a corporation of New Jersey Application October 11, 1949, Serial No. 120,761

4 Claims. 1

This invention relates to impact tools and more particularly to impact tools in which a rotatable hammer strikes and rotates a tool actuating element.

In instruments of this character, there is generally provided an anvil to receive blows struck by a rotating hammer. If the anvil is not in contact with the work which is to be turned, a certain amount of the hammers force is. lost in taking up the looseness or play between the anvil and the work. It is, accordingly, an object of this invention to maintain sufiicient torque on the anvil to maintain contact at all times between the anvil and the work to be turned.

Further objects and advantages of the invention will be in part obvious and in part pointed out hereinafter.

In the drawing which accompanies this specification and in which similar numerals designate similar parts,

Figure 1 is a vertical section through a part of an impact wrench constructed in accordance with the practice of the invention,

Fig. 2 is a horizontal section taken on the lines 22 in Figure 1 looking in the direction of the arrows,

Fig. 3 is an exploded view, in perspective, of the anvil biasing assembly.

Referring to the drawings there is illustrated an impact wrench shown in position for driving a nut It) on a bolt H. In the view shown the motor and gearing end of the machine is not illustrated, not being part of the invention. The wrench comprises a casing I2 within which is suitably journalled a drive shaft l3 adapted to rotate the hammer element It for striking the anvil [5. A bearing l9, in the nose of the casing, is provided for the anvil I which is adapted to extend beyond the casing and which is provided with a square end 28 for attachment to a suitable tool, in this instance a socket wrench 2i fitting the nut it.

Means are provided to convert the continuous rotation of the shaft l3 into intermittent rotation of the hammer element It and to this end there is provided a cup-shaped cam member 22 having a groove 23 forming a repeating V-shaped path around its outer periphery to accommodate balls 24 which also ride in a groove 25 of oppositely disposed V-shape in the interior surface of the hammer I l. The object of the grooves and the balls is to Withdraw the hammer in a longitudinal direction from the anvil. This is normally Opposed by the compressive force of a coil spring 26 tending to force apart the hammer I4 and the cam member 22 so that the balls 24 will normally rest in the apices of the grooves 23-25. The cam member 22 is provided with a hexagonal hole 21 fitting the hexagonal portion 28 of the shaft is. The hammer M is'guided centrally by a shaft or stem 29 having a hexagonal bore 39 to receive the hexagonal end 28 of the driving shaft i3. At its other end the stem 29 is provided with a cylindrical portion 3! rotatably fitting within the longitudinal bore 32 of the anvil l5.

' Adjacent the stem 29 is a thrust bearing 33 adapted to transmit the compressive force of the spring 2% tending to push the cam member 22 away from the hammer It. At its forward end the hammer I 4 is provided with striking faces 36 co-operative with corresponding projections 3? on the anvil [5.

The operation of the hammer and anvil with respect to each other is according to the invention described in Jimerson and Reynolds Patent #2,l60,150 on May 30, 1939. When the resistance of the rotation to the anvil I5 becomes sufficient the hammer Hi is unable to rotate until withdrawn from engagement therewith by the cam action of the grooves 23-25 and balls 24. The rotation of the drive shaft l3 will cause the balls 24 to ride up in the grooves 23 and down into the grooves 25 compressing the spring 26 and storing energy therein. When the hammer M has been withdrawn so that the strikingfaces 35 disengage from the projections 31 of the anvil [5 the hammer I4 is free to rotate. Upon being released its speed is increased beyond the rotational speed of the shaft 13, the energy stored up in the spring 26 then being transmitted to the hammer [4 to provide the increased velocity. As the hammer it rotates ahead of the shaft [3 it again moves forwardly so that its striking faces 36 are in position to strike the projections 31 of the anvil l5 whereupon the action described above is repeated.

In many cases when the anvil i5 is released from engagement with the hammer Hi the reaction normally tends to cause play between the square end 20 of the anvil and the socket 2i as well as between the socket 2! and the nut H]. This play or looseness absorbs a considerable degree of energy by striking of the parts together as the anvil is again struck.

This invention provides an improved means for biasing the anvil E5 in the direction of rotation of the shaft. To this end the stem 29, in the preferred form of the invention, is provided with a friction coupling comprising a ring 38 having a cylindrical bore 39 to fit the portion of the stem 29 adjacent the projections 31 on the anvil I5. Exteriorly, the ring 38 is cut away to form lugs 35 which engage the projections 3'! on the anvil l irrespective of the direction of rotation.

In order to provide frictional contact between the stem 29 and the ring 38 the periphery of the stem portion adjacent the projections 31 on the anvil I5 is provided with a pair of recesses ll. Friction shoes 40 are placed within the recesses ll and when in place achieve rubbing contact with the inner surface 39 of the ring 38. The stem 29 has a pair of holes 42 connecting the recesses 4| in which coil springs 43 reside. The springs 43 force the friction shoes Ml outwardly against the ring 38 thereby assuring firm frictional contact between the stem 29 and the ring 38. Flanges 44 on the stem keep the ring 38 from disengaging from the anvil. In this manner, the ring 38 rotates with the stem 29 unless enough resistance is encountered to cause the ring 38 to slip on the stem 25!.

In the operation of this device the ring 38 rotates with the hammer it, anvil l5, and the stem 23 while the nut is turning easily. When the resistance increases to the point where the hammer i4 is disengaged from the anvil l5, the ring 38 slips on the stem but, because of its frictional contact with the stem, tends to rotate in the direction of the hammer and keeps the anvil firmly against the work thereby preventing looseness from developing between the anvil and the work.

I claim:

1. A friction mechanism for an impact tool comprising an anvil, a rotatable hammer for striking the anvil, a driving element for rotating the hammer, a stem clutched with the driving element, and a friction member constantly in slipping engagement with the stem and in positive engagement with the anvil to tend to rotate the anvil in the direction of the rotation of the hammer when the hammer is rotated.

comprising an anvil, a rotatable hammer for striking the anvil, a driving element for rotating the hammer, a stem positively engaged with the driving element and driven thereby, a ring around the stem in constant positive engagement with the anvil, and a'member on the stem frictionally engaging the ring to tend to rotate the ring in the direction of the rotation of the hammer when the hammer is rotated.

4. A friction mechanism for an impact tool comprising an anvil, a rotatable hammer for striking the anvil, a driving element for rotating the hammer, a stem positively engaged with the'driving element and driven thereby, a ring around the stem in positive and constant engagement with the anvil, a friction shoe on the stem for engagement with the ring, and a spring to maintain engagement between the friction shoe and the ring.

References Cited in the file of this patent UNITED STATES PATENTS Number Name Date 1,933,399 Tranaas Oct. 31, 1933 2,160,150 Jimerson et a1. May 30, 1939 2,408,228 Richards Sept. 24, 1946 2,476,632 Shaif July 19, 1949 2,533,703 Wilhide et a1. Dec. 12, 1950 2,539,678 Thomas Jan. '30, 1951 

